Intravascular administration of fluids is ubiquitous in modern medical practice. These fluids encompass a wide variety, but they are generally water-based. Examples include saline solutions such as "normal saline" or sterile water mixed with sodium chloride to a final concentration of about 0.9%. Other concentrations of saline solution, such as one-half or one-quarter the amount found in normal saline, are also widely used. Further examples of commonly employed intravascular fluids include Ringer's solution, lactated Ringer's solution, and water-based solutions which have other additives. These additives are too numerous to name, but include substances such as potassium chloride, potassium phosphate, glucose or dextrose, magnesium, phosphorus, calcium and many other compounds and elements.
The indications for administering fluids are myriad and are well known in the art. A few of the many indications include dehydration, inability to take fluids by the oral route, and a need for medications which are most efficacious if administered intravascularly. Intravenous fluid administration is more widely practiced than intra-arterial administration, but both are examples of intravascular access to a patient.
Intravenous drug therapy is well known in medical practice. Typically water soluble drugs are used. A few examples of some of the many intravenous medications in use include diuretics such as lasix, cardiac medications such as lidocaine, antibiotics such penicillin and aminoglycosides, hormones such as oxytocin and cortisone, analgesics such morphine sulfate, and chemotherapeutic agents such adriamycin and cis-platinum which are used in cancer therapy. In addition to these drugs and the previously mentioned fluids, intravenous therapy is also widely practiced for transfusions of blood and various blood components such as washed packed red cells and platelets.
Methods of instituting intravenous therapy, such as intravenous fluid or drug therapy, are well known in the art and will only be briefly summarized here. A fluid source, usually a soft-sided plastic bag, contains a sterile fluid suitable for use in humans. The bag includes an access port to which a line or tubing is connected by means which frequently include a cannula. This tubing is in fluid communication with the patient's circulatory system through means which usually include a hollow needle cannula. The needle end is placed into the patient's blood vessel and the opposite end connects to the tubing.
Although intravenous methods are most frequently used for intravascular therapy, intra-arterial therapy is also known and practiced. Because an arterial typically has higher native internal pressure than a vein, there are special problems involved in administering fluids or drugs intra-arterially. Use of an intra-arterial access device typically requires maintenance of higher pressure to deliver fluids as compared to an intravenous method.
When administering intravascular fluids or other substances, it is frequently convenient to include a pumping mechanism along the line or tubing. This pump, which is often a peristaltic-type pump, assists in delivering a precise volume at a specified rate. If a pump is not used, some other flow monitoring means are used. For instance, the clinician or assistant may rely on gravity to create a pressure differential between the bag and the patient's vascular access to achieve flow. This usually consists of placing the bag or fluid source higher than the level of the entry point of the fluid into the patient. A rotatable knob at the exit portion of the bag is manipulated to control egress of the fluid. The pump method can be more accurate and reliable in delivering the desired flow.
The pump generally involves a gear mechanism including rollers which accept the intravenous tubing. Pressure of the rotating rollers squeezes or milks the tubing to allow flow of fluid from the fluid source to the patient. Usually the tubing is curved over the gear mechanism which is covered by a door. The typical arrangement is that when the door is opened the tubing is not compressed at the point where the tubing enters the pump and thus free flow of the fluid is temporary permitted. Unfortunately it is frequently necessary to open the door to adjust the tubing or to solve some problem which has caused the machine to emit a warning beep or light. During this time, that is, when the door is open, there exists a risk of inappropriate fluid flow from the fluid source to the patient. Additional compromise can occur if the door is inadvertently left open or is not completely closed. This inadvertence can lead to inaccurate dosing of the fluid or medication contained in the fluid. Because the fluid flow is less restricted when the door is open than when the door is shut, inadvertence in leaving the pump door open would lead to overdosage of the patient with the fluid or medication.